In the remarkable development in precision machining over these years, 100 nm or less minute diamond abrasives have come into use. The trend towards smaller particle sizes may call for further minute diamond abrasives of, say, 10 nm or so particles within a few years. As prospective, diamond powders of this level of size are also an object of studies for new applications including additive to lubricant, carrying medium for inspecting or medicating chemicals, etc.
Diamond products of a size under 100 nm are commercially available from, as known, such processes, first, that graphite is converted, under ultrahigh pressure and high temperature to diamond crystals, which then are crushed into smaller sizes, and second, that a carbonaceous ingredient is converted to diamond under ultrahigh pressure and high temperature produced by the detonation of a high performance explosive with high content of carbon.
The graphite converted diamonds described above include one that is single crystalline, produced statically on a hydraulic press, and another that is polycrystalline, also referred to as Du Pont type diamond, produced dynamically by explosion of an explosive chemical. The former technique can yield coarse particles of a size over 0.5 mm, while the latter often produces over 100 nm secondary particles, which are fused agglomeration of around 10 to 30 nm spheroidal primary particles, as a result of too short the pressure loading period for the crystals to grow, which lasts just a few microseconds. The diamond originating from an explosive is referred to as “detonation diamond”, which is normally in the form of over 100 nm secondary particles of firm agglomeration of 4 to 10 nm primary crystallites.
Those diamonds can be reduced in size by crushing the graphite converted diamond or by chemically processing the explosive converted diamond, into particles of 10 nm or less, to be suspended in water. However no efforts have been tried for sorting and isolating diamond particles of sizes less than 10 nm or less than 20 nm.